1. Copyright Notice
This patent document contains information subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent, as it appears in the U.S. Patent and Trademark Office files or records but otherwise reserves all copyright rights whatsoever.
2. Field of the Invention
The present invention, in certain respects, relates to enterprise storage systems and backup and recovery processes. In other respects, the present invention relates to performing a split or break of a mirror disk from a primary disk in preparation for a file level backup of files from the mirror disk to a secondary long-term storage device, such as a tape backup device.
3. Description of Background Information
Enterprise storage systems store data for enterprise level applications, and thus play a critical role in many business environments. A company may use an enterprise storage system to migrate its disparate and separately located data centers to a new central location. In addition, an enterprise storage system can form a key part of an infrastructure that allows an internet service provider (ISP) to store, manage, and deliver rich media content, that gives the ISP backup and restore capabilities essential for site failures or disasters, and that allows the ISP to streamline its management of hardware and software platforms and applications.
In such business environments, and in many others, the data used is mission-critical. Enterprise storage systems provide enterprise level systems with fast (low latency) read and write access to media (typically magnetic disks) suitable for storing such mission critical data, and meanwhile protect the data and make it continuously available even when a primary disk holding the data fails. To help with such protection and continuous availability, enterprise storage systems are typically provided with mirror disks (or volumes) that provide redundancy for a primary disk (or volume). Such a mirror may be implemented in the form of a standard RAID mirror. An additional mirror may be provided for additional data protection, or may be provided instead of a standard RAID mirror. An EMC Symmetrix™ storage unit may serve as an enterprise storage system, comprising a primary disk and a mirror disk; in this context, the mirror disk is referred to as business continuance volume (BCV). The enterprise storage system may comprise two Symmetrix storage units, including a first Symmetrix storage unit (having a primary disk) connected to a second Symmetrix storage unit (having a mirror) by a high speed data link; here, the mirror is referred to as a Symmetrix Remote Data Facility (SRDF)™ volume. A volume is a storage entity that might correspond to a portion of a hard disk or a group of hard disks within a given enterprise storage platform.
Enterprise storage systems such as those described above perform data backup processes and restore processes. Disk level backups and restores involve the backing up or the restoring of a raw “image” of the entire disk, while file-level backups and restores require file mapping, a process by which each file to be backed up, that may be located at various physical locations on a disk (or separate disks) is mapped (i.e., tracked using meta data) when it is sent to the backup storage devices.
Mirrors may serve different purposes. For example, a mirror may provide redundancy for a primary disk, when there are problems with the primary disk, in which case the host can be given direct access to uncorrupted data on the mirror. Mirrors also facilitate mirrored restore and mirrored backup operations. Data may be restored, for example, from a backup storage device with or without mirroring. With a mirrored restore, data is typically first read from the backup storage device and stored onto a mirror disk, and later moved from the mirror disk to the primary disk for use by the host system. With a mirrored backup, data on the primary disk is first synchronized onto the mirror, and later moved from the mirror to the backup storage devices.
When performing operations involving a mirror disk, it is frequently necessary to perform certain actions on the mirror. For example, a mirror may be established, split, or synchronized in either direction (including a synchronization from the mirror to the disk, and a synchronization from the disk to the mirror). When a mirror is established, changes in the data content of a primary disk are also applied to the data content on the mirror disk, thereby maintaining a “mirror image” of the primary disk on the mirror disk. When a mirror disk is split, changes in the data content of the primary disk are no longer applied to the data content of the mirror disk.
An example mirror split process is shown in FIG. 2. Before the mirror disk is split, as shown in act 40, it may be updated, when necessary, to represent the data content of the primary disk at a time just prior to the split, and in act 42 the mirror disk is then split, i.e., logically detached from the primary disk and made addressable to the host system. A BCV mirror of a Symmetrix storage unit, when it is split, is assigned to an original device address used by the host system.
When a mirror is synchronized, synchronizing data from the primary disk to the mirror, all of the changes that have occurred to the data on the primary disk are applied to the mirror disk, in order to bring the mirror disk current with the primary disk. Similarly, in the opposite direction, when synchronizing data from the mirror disk to the primary disk, changes to data on the mirror disk are applied to the primary disk so that the primary disk matches the mirror disk. This mirror disk to primary disk synchronization is often one of the final steps that occurs during a mirrored restore operation, where data is restored from the backup storage devices to the primary disk.
Mirror splits are performed whenever there is a need to make either the mirror disk or the primary disk accessible to another entity independent of the other of the two disks. The sooner the split can be finished, the sooner both disks are independently accessible. For example, when a file level mirrored backup occurs, data is synchronized from the primary disk to mirror disk while the application in the host is quiesced (e.g., frozen or placed in a hot backup state) (this is referred to as a database outage). Individual files to be backed up are then copied from the mirror disk to the backup storage device while, after a database quiesce period, a database application on a host system can freely read from and write to a database stored on the primary disk.
FIG. 4 provides waveforms depicting the timing of certain operations pertinent to a file level mirrored backup. Waveforms (a) and (b) correspond to a background file level mirrored backup operation. Waveform (a) depicts the timing of quiesce 400 and backup 402 operations, and waveform (b) depicts the timing of extent mapping 406 and of a database outage 406. In such a background system, data is backed up for a period of time 402, after the database is quiesced 400. During the backup, data is moved (or copied) from the mirror disk to the backup storage devices; as the data is moved from the mirror disk to the backup storage devices, a database outage 404 may last too long.
A database outage with such a background approach can last, for example, up to six minutes. In certain business environments, this can present a significant inconvenience to users of a given computer system. For example, if a Microsoft Exchange Server is being backed-up, this can prevent users from using Microsoft Outlook during a substantial portion of the backup process.